1. Field of the Invention
The present invention relates to a camera which is capable of reading in film specific information such as ISO sensitivity or the like from a bar code which is rotating together with the rotation of a cartridge spool which is housed within a film cartridge.
2. Description of the Related Art
A film cartridge has been disclosed, for example in U.S. Pat. No. 5,025,274, in which film specific information such as ISO sensitivity or the like is displayed in bar code form by being inscribed on a disk which rotates together with the rotation of a film spool which is housed within the film cartridge. FIGS. 7(a)-(c) shows an exemplary such prior art type film cartridge.
In FIG. 7(a), the reference numeral 301 denotes a bar code which encodes information specific to the film in this film cartridge, said film specific information including (but not being limited to) ISO sensitivity of the film, while 302 denotes an ISO code plate on the upper surface of which in the figure said bar code is inscribed. This ISO code plate 302 is fixed to a film spool 303 which is housed within the film cartridge, and rotates as one body together with said film spool 303.
Generally the bar code 301 consists of a number of rod shaped black colored portions of a black color or the like having relatively low reflectivity which are disposed against a background consisting of a predetermined region of a white color or the like having relatively high reflectivity, and the desired information is encoded according to the number and the widths of these black colored portions and according to the number and the widths of the white colored remainder regions left between these black colored regions. Accordingly it is possible to read out the information which is encoded in said bar code by reading out the distribution of reflectivity from the bar code over a line which extends across the bar code 301. In the example shown in FIGS. 7(a)-(c), since the bar code 301 is inscribed around the ISO code plate 302 in the circumferential direction around the central axis of the film spool 303, it is possible to read out the information which is encoded in said bar code 301 by reading out the distribution of reflectivity following a line which extends in the circumferential direction around the upper surface of said ISO code plate 302.
As shown in FIG. 7(b), the ISO code plate 302 is affixed to the film spool 303 and a film 304 is wound upon the film spool 303, all of them then being further housed within a film cartridge 305 as shown in FIG. 7(c). A cut away portion 306 is formed through the upper surface of the film cartridge 305, and the upper surface of the ISO code plate 302 is exposed to view from the outside through this cut away portion 306. When this film cartridge 305 is loaded into a camera not particularly shown in the figure, a film forwarding device (not shown either) can rotate the film spool 303 within said film cartridge 305 either so as to project the film 304 out from said film cartridge 305 or so as to rewind said film 305 back within said film cartridge 305, and when this happens, since the ISO code plate 302 rotates together with the film spool 303, it is possible to read out the film specific information relating to ISO sensitivity or the like which is encoded in the bar code 301 via the cut away portion 306 in the film cartridge 305.
Since the upper surface of the ISO code plate 302 is exposed to view from the outside through the cut away portion 306, if a photoreflector is used which is made up from the combination of a light emitting element which illuminates the bar code 301 on the ISO code plate 302 via the cut away portion 306 and a light receiving element which receives the reflected light from said ISO code plate 302 again via said cut away portion 306, it is possible to read out the film specific information encoded in the bar code 301.
However, with a film cartridge according to the above described prior art, when the bar code 301 inscribed on the upper surface of the ISO code plate 302 is being read out, problems can occur which will now be described with reference to FIGS. 4 (a) through 4 (f).
FIG. 4(a) shows a perspective view of the ISO code plate 302 which is housed within the film cartridge 305. The circumferentially extending line A in this FIG. 4(a) is the so called readout line, which is traced when the bar code 301 is read out via the cut away portion 306 in the film cartridge 305 as the ISO code plate 302 is rotated within said film cartridge 305 about its central axis along a direction denoted by X in the figure.
FIG. 4(b) is a figure showing the bar code 41 displayed in linear form corresponding to the readout line A of FIG. 4(a). This FIG. 4(b) line from its left end to its right end corresponds to the bar code which is read out when the ISO code plate 302 is rotated through exactly one full revolution.
FIG. 4(c) is an enlarged view of the left end portion of the bar code 301 shown in FIG. 4(b). When this bar code 301 is read out using the above described photoreflector (not shown), the output signal from the photoreflector is high level when the white colored portions of said bar code 301 pass said photoreflector since their reflectivity is relatively high, while on the other hand said output signal from said photoreflector is low level when the black colored portions of said bar code 301 pass said photoreflector since their reflectivity is relatively low.
FIG. 4(d) is a waveform diagram showing the output from the photoreflector when the bar code portion in FIG. 4(c) is correctly read out. When the bar code 301 is correctly read out, the output signal from the photoreflector when the white colored portions of said bar code 301 pass it is sufficiently high, and furthermore the output signal from the photoreflector when the black colored portions of said bar code 301 pass it is sufficiently low, and accordingly, if a threshold level shown in the figure by "Y" is chosen which is substantially half of the maximum value, it is easily possible to determine which are the white colored portions of the bar code and which are its black colored portions.
However it is not possible to read in the bar code 301 accurately if as shown in FIG. 4(e) the overall output from the photoreflector is unduly low. It can happen that the overall output from the photoreflector is unduly low because the battery which serves as the power source for the photoreflector is nearly exhausted, or because the printing of the white colored portions of the bar code 301 on the ISO code plate 302 is poor so that their reflectivity is relatively low, or for other reasons. When the overall output from the photoreflector is unduly low, if the threshold level Y is set to be the same as in the case of FIG. 4(d), the output of the photoreflector which corresponds to the white colored portions of the bar code 301 remains lower than this set threshold level Y, and the bar code 301 cannot be read in accurately because it is determined to consist entirely of black colored portions.
On the other hand, if as shown in FIG. 4(f) the overall output from the photoreflector is unduly high, it is not possible to read in the bar code 301 accurately either. It can happen that the overall output from the photoreflector is unduly high because the battery which serves as the power source for the photoreflector is brand new, or because the printing of the black colored portions of the bar code 301 on the ISO code plate 302 is poor so that their reflectivity is relatively high, or for other reasons. When the overall output from the photoreflector is unduly high, if the threshold level Y is set to be the same as in the case of FIG. 4(d), the output of the photoreflector which corresponds to the black colored portions of the bar code 301 remains higher than this set threshold level Y, and the bar code 301 cannot be read in accurately because it is determined to consist entirely of white colored portions.
As explained above, in the case of a film cartridge of the type in which film specific information such as the ISO sensitivity value or the like is encoded by means of a bar code such as the bar code 301, the problem can happen, when the bar code 301 is read out by means of a photoreflector, that there is a possibility that the film specific information cannot be read out correctly, due to variation in the output of the photoreflector.